A common problem with these camera's is that in the contact within the camera springiness resulting in one of the batteries sitting 2mm lower than it should and not getting a good sitting.
Ideally this should be fixed properly (idea for a ifix walkthrough) but I've not been prepared to do this as yet and settled for a workaround fix which I posted about and is already linked on this site (also below)
[http://lakeuk.blogspot.com/2010/04/camara-fix.html|Camera Contact Fix]